Solid state imagers are increasingly popular due to small size, low cost, and improved image quality. One such solid state imager is a CMOS imager. CMOS sensor technology enables a higher level of integration of an image array with associated processing circuits, which can be beneficial to many digital applications such as, for example, in cameras, scanners, machine vision systems, vehicle navigation systems, video telephones, computer input devices, surveillance systems, auto focus systems, star trackers, motion detection systems, image stabilization systems and other imaging applications.
A CMOS imager circuit includes a focal plane array of pixel cells, each one of the cells including a photosensor, for example, a photogate, photoconductor or a photodiode overlying a substrate for accumulating photo-generated charge in the underlying portion of the substrate. Each pixel cell has a readout circuit that includes at least an output field effect transistor formed in the substrate and a charge storage region formed on the substrate connected to the gate of an output transistor. The charge storage region may be constructed as a floating diffusion region. Each pixel may include at least one electronic device such as a transistor for transferring charge from the photosensor to the storage region and one device, also typically a transistor, for resetting the storage region to a predetermined charge level prior to charge transference.
In a CMOS imager, the active elements of a pixel cell, as just described, perform the necessary functions of: (1) photon to charge conversion; (2) accumulation of image charge; (3) resetting the storage region to a known state; (4) selection of a pixel for readout; and (5) output and amplification of a signal representing pixel charge. The charge at the storage region is typically converted to a pixel output voltage by the capacitance of the storage region and a source follower output transistor.
CMOS imagers of the type discussed above are generally known as discussed, for example, in U.S. Pat. No. 6,140,630, U.S. Pat. No. 6,376,868, U.S. Pat. No. 6,310,366, U.S. Pat. No. 6,326,652, U.S. Pat. No. 6,204,524 and U.S. Pat. No. 6,333,205, assigned to Micron Technology, Inc., which are hereby incorporated by reference in their entirety.
Due to the sensing capabilities of CMOS and other solid state image sensors, such sensors can be used as analytical devices. Based on advantages such as low-cost production and lower power consumption, CMOS image sensors may be particularly well suited for this purpose. The analytical devices can be useful for a range of applications, including clinical screening, detection of environmental contaminants, and gene hybridization.
There are known examples of using luminescent bioreporters that include CMOS integrated circuits. For example, in U.S. Pat. No. 6,905,834, bioluminescent bacteria are placed on specially-designed integrated circuits that include CMOS pixel sensors, each with a photodiode. The bacteria are designed to produce a luminescence in response to metabolizing a targeted substance. The CMOS pixel sensors are capable of sensing the incoming luminescence and converting it to a digitized, output signal. These bioreporters can be used for detecting a variety of substances.
While the devices discussed in U.S. Pat. No. 6,905,834 have potential for application in a number of contexts, the use of bacterial substances may make the disclosed bioreceptors less desirable in other contexts. In addition, depending on the source of the bacteria, the disclosed bioreceptors could be costly to produce and may have a limited shelf-life. In addition, these bioreceptors are designed using materials that fluoresce (i.e., put out light) when exposed to certain substances. Thus, these devices are limited in the materials that can be used for detection and in the substances that they can be used to detect.
Thus, it is desirable to have an analytical device, using solid state image sensors, for example, CMOS sensors, to detect and report reactions, such as exposure to a compound under test, that can be useful with a vast number of compounds and that can be easily and cost-effectively produced. Simple methods of fabricating the analytical devices are also needed.